1. Field of the Invention
This invention relates to a manipulation technique for valves of oil well test strings.
2. Description of the Prior Art
Annulus pressure responsive (hereafter called "APR") test-string manipulation is a relatively recent development in the art of oil well formation testing. U.S. Pat. No. 3,664,415 to Wray and Petty, assigned to the assignee of this invention, in 1972 disclosed a formation testing method and apparatus using variations in well annulus pressure to control the valving operation of a testing tool to entrap a formation sample. In formation testing, it is desirable to have a circulation valve, so that excess formation fluids present in the test string after testing may be forced out by pumping drilling mud or other displacement fluid down the well annulus and into the interior of the test string through the reverse circulation valve and upward toward the surface through the interior of the test string. This operation is called "reverse circulation."
A circulation valve is also desirable to allow a flow path for fluids trapped in a test string above a closed valve, such as a tester valve for taking closed-in pressures, so that such fluids may pass into the wellbore upon pulling the pipe string from the well. This avoids having to contend with such well fluids at the wellhead. It would be a most disagreeable task to have to separate thousands of feet of pipe sections full of well fluids due to the absence of a properly functioning reverse circulation valve capable of allowing the fluids to "dump" into the well as noted above.
Four types of reverse circulation valves are currently used in test strings: the rotating valve, the impact-sub valve, the reciprocal valve and the pump-out plug valve.
The rotating valve is operated by rotation of the test string to open a reverse circulation port. This requires opening of blow-out preventer rams and rotating the pipe, which can be difficult if the pipe is in a bind as in the case of a deviated hole, and which could be catastrophic should the well "blow" during the rotational operation. Likewise, a reciprocally operated valve is subject to difficulties in deviated holes.
An impact-sub type circulating valve requires dropping a bar which might hit ledges inside the pipe or have to fall through very viscous fluid and such a sub must be placed above any blind-type valve in the string.
The pump-out type circulating valve might require internal pressure significantly higher than annulus pressure in order to open. In cases where annulus pressure is already high, such as where APR test tools are used, or it is undesirable to load the running string for hydraulic pressure application, a pump-out type valve might not be desirable.
Considering said limitations, APR circulating valves have been developed to overcome the above noted difficulties, which are especially important in offshore oil well formation testing, and so as to be compatible with other APR testing tools and operable by essentially the same surface equipment.
One solution to the above problems is a pressurized gas-biased annulus pressure responsive reverse circulating valve operated by multiple pressurizations and depressurizations of the well annulus as disclosed in pending application Ser. No. 288,187 by Holden et al., filed Sept. 11, 1972, now U.S. Pat. No. 3,850,250 issued Nov. 26, 1974 and assigned to the assignee of this application.
Another solution to the above problems and others is provided by the apparatus of the present invention, which provides a simple, inexpensive, reliable APR valve.